This question is actually two completely different questions wearing the same words, and mixing them up causes real confusion (and occasionally real danger):
- “How far should my PORTABLE generator run from the house?” Answer: 20 feet or more from every window, door, and vent, exhaust pointed away — a carbon monoxide rule, absolute, with no engineering workaround.
- “How far must my STANDBY generator be installed from the house?” Answer: as close as 18 inches from the wall in many listed installations — but at least 5 feet from openings (windows, doors, vents), plus service clearances and local setbacks — a fire-code and exhaust-management rule with real nuance.
Yes, you read that right: the permanent unit can legally sit a foot and a half from your siding while the portable must stay twenty feet out. The difference isn’t bureaucratic inconsistency — it’s engineering, and understanding it will make you better at placing either machine. This guide covers both rulebooks, why each number exists, and the placement strategy that can shave $1,500 off an installation quote.
Rulebook 1: Portable Generators — The 20-Foot CO Rule
For portables, distance is a life-safety rule, not a code detail:
- 20+ feet from the house — measured to every opening: windows (closed ones leak), doors, soffit and dryer vents, AC intakes. The CPSC’s floor, born from post-storm death investigations [→ /portable-generators/portable-generator-safety-carbon-monoxide/].
- Exhaust pointed away from your home and the neighbors’ — distance sets the baseline; direction decides where the plume concentrates.
- Never inside anything: garage (open door included), basement, porch, breezeway, shed. The 20-foot rule has no indoor version.
- The practical kit that makes 20 feet easy: heavy-gauge cords sized for the run (12-gauge to 50 ft, 10-gauge beyond [→ /portable-generators/what-size-generator-runs-refrigerator/]), a running canopy for weather [→ /portable-generators/run-generator-in-rain/], and a ground anchor for theft.
Why so far, when the standby sits at 18 inches? Because the portable’s exhaust exits low, unducted, at ankle height, in whatever direction the machine happens to face — while the standby’s exhaust system is engineered, directional, tested, and listed for close installation. Which brings us to rulebook two.
Rulebook 2: Standby Generators — The Clearance Map
A standby unit’s placement is governed by overlapping requirements — national fire standards, the manufacturer’s listing, and local amendments. The commonly applied numbers:
| Clearance | Typical requirement | Why it exists |
|---|---|---|
| From the house wall | 18 inches minimum (per most major manufacturers’ listed installations) | Fire standard compliance + service access + engineered exhaust direction |
| From windows, doors, vents, and any opening | 5 feet minimum | Exhaust (CO) must not enter the building — the standby version of the 20-foot rule |
| Service clearance around the unit | 3 feet clear (5 ft in some jurisdictions/manuals) | Technician access + cooling airflow [→ /standby-generators/how-long-do-whole-house-generators-last/] |
| Above the unit | 3–5 feet to overhangs/deck undersides | Heat + exhaust rise |
| From combustible materials/vegetation | Per manual — typically 3+ feet, more in wildfire country | Hot surfaces + fire spread |
| From gas meters/regulators and AC condensers | Utility- and code-specified separation (commonly ~3 ft; utilities vary) | Ignition-source separation |
| From property lines | Local zoning setback — commonly 3–10 feet, highly variable | Noise + access + fire spread to neighbors [→ /portable-generators/how-loud-are-generators/] |
Three notes that keep those numbers honest:
- The 18-inch figure is a listed-installation allowance, not a universal right. It rests on national fire-standard provisions for units tested and listed for close placement (which the major residential brands are) beside non-combustible or protected walls. Vinyl siding, unusual wall assemblies, or a local amendment can change the answer — one of several reasons the site survey and permit exist [→ /installation-costs/generator-permit-requirements/].
- The 5-foot openings rule is the one inspectors measure with a tape. Every window within range gets counted — including the basement window you forgot and the bathroom vent above. Serious storm-state jurisdictions are strictest here, correctly.
- Local amendments override everything general. Coastal wind-zone anchoring, wildfire-country vegetation clearances, historic-district reviews, and plain municipal preference all layer on top. Your installer’s jurisdiction knowledge — verified by your ten-minute building-department check — is the tiebreaker [→ /installation-costs/generator-installation-cost/].
Placement Strategy: Where the Rules Meet Your Wallet
Within the legal envelope, placement is the highest-leverage cost and livability decision of the whole install — decided in ten minutes at the survey and lived with for twenty years:
1. The golden triangle: panel + gas meter + pad. Every foot between the generator and your electrical panel is conduit and labor; every foot to the gas meter is pipe and possibly trench. The pad location that shortens both runs can cut $1,000–$2,500 from a quote — sometimes a 10-foot rethink versus the “obvious” spot [→ /installation-costs/generator-installation-cost/]. Ask the surveyor to price two placements; the comparison costs nothing.
2. The noise map. The unit will hum at 60–70 dB weekly (self-test) and for days during outages — so within the legal envelope, favor: away from bedroom windows (yours and the neighbors’), behind the garage or a masonry mass, exhaust end toward open space [→ /portable-generators/how-loud-are-generators/]. The clearance rules give you a minimum distance from openings; sleep gives you a reason to exceed it.
3. The service reality. A technician visits yearly for two decades [→ /standby-generators/how-long-do-whole-house-generators-last/] — the legally-required 3 feet of clearance should also be pleasantly reachable (not behind a locked fence section or a future hot tub). Landscaping plans count: today’s 3-foot clearance is tomorrow’s hedge violation.
4. The water and snow audit. Not on the drainage path, not under the roof valley’s waterfall, not where the plow berm lands, elevated per the manual on its pad — flooding and burial are leading causes of “standby generator failed during the event” stories.
5. The wind-zone extras (coastal): hurricane jurisdictions add engineered anchoring and sometimes elevated platforms in flood zones — real costs the survey should surface, not the change order [→ /standby-generators/generator-buying-mistakes/].
Frequently Asked Questions
How far does a portable generator need to be from the house? At least 20 feet from every window, door, and vent, with exhaust pointed away — the CPSC carbon-monoxide rule. More distance costs a longer heavy-gauge cord and buys wind margin; there is no compliant indoor or attached-structure placement.
How close can a standby generator be to the house? As close as 18 inches from the wall in listed installations from major brands — while maintaining at least 5 feet from any window, door, or vent, roughly 3 feet of service clearance, and whatever local amendments add. The site survey and permit confirm your specific answer.
Why can a standby generator be closer than a portable? Engineering and testing: standby units have directional, engineered exhaust systems and are listed for close installation beside protected walls. A portable’s low, unducted, omnidirectional exhaust gets no such credit — hence 20 feet.
How far does a generator need to be from a window? Portable: 20+ feet, like every opening. Standby: 5 feet minimum from any operable window, door, or vent — the measurement inspectors take most seriously, basement windows included.
How far should a generator be from the gas meter? Separation from meters and regulators is utility- and code-specified — commonly around 3 feet, but utilities vary and some require more. Your installer coordinates this during the gas verification that belongs in writing on every quote [→ /installation-costs/generator-installation-cost/].
Can a generator go under a deck or overhang? Portables: never — that’s an enclosure. Standby units: only with the manual’s specified overhead clearance (typically 3–5 feet to combustible surfaces) and never beneath openings; many installers simply decline deck placements, and flood/snow logic usually agrees with them.
The Bottom Line
Two machines, two rulebooks: the portable lives by one absolute — 20 feet from every opening, exhaust away, never enclosed — while the standby lives by a clearance map (18 inches from the wall where listed, 5 feet from openings, 3 feet of service space, plus your town’s layer) that a survey and permit turn into your specific answer. Learn both, then spend your actual decision-making on the placement strategy: the pad spot that shortens the panel and gas runs, spares the bedrooms, drains dry, and welcomes the technician is worth $1,500 at the quote and twenty years of not thinking about it afterward [→ /installation-costs/generator-installation-quotes/].